There are numerous cases of ferrierite synthesis described in the literature. Ferrierite has been synthesized from gels free of organic structure directing agents (“OSDA”), or templates, as shown in U.S. Pat. Nos. 3,933,974; 3,966,883; 4,088,739; and 4,650,654. Typically, synthesis of ferrierite in the absence of OSDAs does not provide good control of the crystal size and morphology.
Various OSDAs, specifically nitrogen-containing organic compounds, have also been employed in the synthesis of high purity ferrierite. Some examples include U.S. Pat. Nos. 4,000,248; 4,016,245; 4,251,499; 4,377,502; and 4,795,623. The use of organic templates allows for a decrease in the crystallization temperature and time, as stated in U.S. Pat. No. 4,000,248. U.S. Pat. No. 5,491,273 describes the synthesis of ferrierite crystals or around 0.5 microns and larger using pyrrolidine as the structure directing agent.
U.S. Pat. No. 6,136,289 describes the synthesis of ferrierite from organic-free gels containing boric acid. Ferrierite crystals of 0.5 micron size and larger were formed.
Pinar et al. (Collection of Czechoslovak Chemical Communications, vol. 72 (2007) pp. 666-78) showed a strong influence from tetramethylammonium (“TMA”) cations on the crystallization of ferrierite from gels containing 1-benzyl-1-methylpyrrolidinium cations as the primary OSDA. Ferrierite crystals having an average size of about 10 microns were obtained. However, quartz was present in the synthesized ferrierite samples.
Roman-Leshkov et al. (Journal of Physical Chemistry C, vol. 115 (2011) pp. 1096-102) described the synthesis of ferrierite from a mixture of TMA and a cyclic amine having a different ring size. Thin plate-like crystals having a size over 1 micron were formed.
Nishiyama et al. (Microporous Materials, vol. 12 (1997) pp. 293-303) showed that ferrierite needle-shaped crystals having an average diameter of 30 nm were formed in the cavities of a porous alumina support. The important aspect of their work was that the crystal growth and size were physically constrained by the pore size of the support rather than the reaction gel composition or the crystallization conditions during the synthesis. This is further supported by the fact that the ferrierite crystals formed on the external surface of the porous alumina support had a size on the order of micrometers.
Khomaine et al. (Journal of Colloid and Interface Science, vol. 236 (2001) pp. 208-13) showed that by using varying amounts of a non-ionic surfactant in addition to a pyrrolidine template, the size of ferrierite crystals could be controlled in a range between 1 and 3 micrometers.
Chauhan et al. (Indian Journal of Chemical Technology, vol. 18 (2011) pp. 335-42) studied the effect of several cationic, anionic, and non-ionic emulsifiers on the crystallization of ferrierite.
In view of the foregoing, there is a need for a method of making a highly crystalline, small crystal ferrierite zeolite. It has been found that a synthesis process that includes a mixture of silica and alumina sources with water and an alkali source, as well as a combination of two organic structure directing agents, solves the foregoing need.